1. Field of the Invention
The present invention relates to a method and apparatus for initiating a spindle servo in an information recording disk regenerating apparatus.
2. Description of the Prior Art
A disk regenerating apparatus regenerates information from a recording disk (hereinafter simply called "disk") such as a video disk. Typically, a video signal, recorded on such a video includes video information such as a composite image signal or the like or a digital audio signal is recorded with a compressed time base. A similar digital audio disk has a special regenerating mode or a so-called scan operation requiring a jump operation for jumping the spotlight for reading recorded information of the disk from one track to another track one or more pitch away in addition to a normal sequential regenerating mode.
In the disk regenerating apparatus, there exists a fluctuating component of the time base due to irregular rotation or other defect of a spindle motor whereby the disk is driven to rotate with a regenerative signal obtained through a pickup. To suppress the time base fluctuation, the so-called spindle servo is used. For the spindle servo, a conventional arrangement is such that a regenerative synchronizing signal such as horizontal synchronizing pulse or the like is extracted from the regenerated video signal. A phase difference between the regenerative synchronizing signal and a reference synchronizing signal generated in the apparatus is detected and the rotational frequency of the spindle motor is controlled so as to minimize the phase difference. For the jump operation, on the other hand, the spotlight is controlled to follow a recording track of the disk, i.e., a servo loop of the tracking servo opens up during jumping and thus the regenerative synchronizing signal cannot be obtained. Therefore control on the spindle servo has not hitherto been made during the time period of jumping.
In such a disk regenerating apparatus, where a so-called CLV (constant linear velocity) disk is jumped across tracks during regeneration, the disk is changed in speed according to a radial disk position of the pickup. Accordingly, a control is not given at any time that the tracking servo loop is kept open. Thus, in a prior art control system in which the servo is initialized after the loop closes, a considerably long time is required before the spindle servo system is stabilized.